This invention relates to elevators which store electrical energy in an energy storage system during a regenerative mode of operation. In particular, the present invention relates to a thermal management system using thermoelectric heating and cooling to maintain the energy storage system in a desired operating temperature range.
Regenerative elevator systems include a regenerative mode of operation which generates power during certain times of elevator operation. During the regenerative operation, the regenerative drive of the elevator produces electricity, which is stored in energy storage devices through a charging circuit. The energy storage devices are typically batteries, although other devices such as super capacitors may also be used as part of an energy storage system.
The batteries used in the energy storage system of a regenerative elevator tend to be expensive components. Achieving satisfactory battery lifetime, therefore, is an important consideration. The lifetime of a chemical energy storage device such as a battery typically decreases exponentially with rising temperature.
A battery generates heat due to ohmic resistance of the battery and the exothermic effect arising from the combination reaction of the substances generated at the anode and cathode during over-charging processes. Elevated temperature accelerates deterioration of the battery. In particular, local heating of some of the cells in series in the battery can cause dramatic reduction of system reliability since unbalanced deterioration of a single cell can lead to propagation of failure in a chain reaction fashion.
When an elevator is in its regenerative mode, the energy generated is used to charge the batteries of the energy storage system. The temperature of the storage system rises during charging. With higher charging rates, which are typical for the regeneration mode, the temperature rise can be pronounced.
Too low an operating temperature also adversely affects the energy storage system. A low ambient temperature reduces the specific power of the battery and thus reduces the amount of stored energy that can be extracted from the battery. Thus lower operating temperatures can reduce the operability of the elevator system and affect the ride quality of the elevator.
The energy storage system for regenerative elevators may be located in the machine room or in the hoistway, where the temperature can vary widely because those locations are not air-conditioned. A new approach to temperature control for the elevator energy storage system is needed.